The present invention relates to a process for the readjustment or resetting of the trajectory or path of a member actuated for automatically following a line described with respect to an object, as well as to an apparatus for performing this process.
The invention more particularly deals with the problem of resetting the path of a welding head with respect to a joint constituted by the juxtapositioning of two parts. However, this application is not limitative and the invention can be used for solving any other problem connected with the resetting of the path of a member with respect to a line described relative to an object.
The invention can consequently equip all industrial robots requiring a precise positioning of a member along a line described relative to an object and whose position can be detected by a sensor.
The development of robotics corresponds to the need to increase production in all industrial fields, where the flexibility of the robot is utilized for adapting to certain production types on large batches or lines. This development consequently corresponds to the reduction of organisational and planning constraints linked with the production of small and medium size batches or lines. Finally, robotics makes it possible to solve problems produced by unhealthy or dangerous working conditions.
Industry has a great need for such highly developed handling, manipulating or production means. In particular, arc welding, with or without a filler metal, leads to several specific problems making it necessary to develop automatic machines or robots suitable for this procedure. In the welding field, it is often necessary to follow the joint to be welded between two metal sheets with a very high degree of precision, while this must take place in fast and reproducible manner. Thus, it is known that the assembly, by welding, of a large number of elements with a high degree of precision and without any possibility or repair or error, requires highly skilled, difficulty obtainable, manpower. It is often impossible to ensure intense production, due to the fatigue and physical constraints resulting from the precision required. When the parts to be welded are very large, it is often necessary for them to be preheated prior to welding, which makes it necessary for the welder to wear protective clothing in order to approach them. Thus, unhealthy and dangerous working conditions occur. When welding is carried out between heat-deformable elements, any automatic welding machine or robot programmed to a very accurate path cannot adapt to these deformations, which can reach several centimeters in certain cases.
It is then necessary to provide means for bringing the member onto the line to be followed which differs, due to these deformations, from the stored or preset path. The Applicant has proposed in French Patent No. 8,005,909 filed on Mar. 17, 1980 a process for the positioning of a member relative to a metal surface and to a line formed on said surface. According to this earlier invention, a member is displaced by a robot along a stored path and is automatically reset by an auxiliary device inserted between the end of the robot and the member to a predetermined value with respect to the distance separating the member from the surface and the lateral displacement of said member with respect to a line formed on said surface.
In order to bring the member onto the line to be followed, a position detector is added thereto, which informs the system of the value of the aforementioned quantities. Servocontrol means are provided to bring the member from its real position, which is a function of the stored trajectory, to its correct position, which is defined by the predetermined values. This path following process involves bringing the member permanently onto the path to be followed, when the latter differs from the stored path.
The process of the invention is of a different type and consists of resetting the member before following the stored path. To this end, it comprises a position detector and means controlling a movement of the member relative to the carrier of said member in accordance with at least one direction contained in a plane transverse to the forward movement direction of the member.
Complex robots are known making it possible to reset paths on a line to be followed and which can move in a parallel or non-parallel manner to the stored line. This can be obtained by having a direct action on all the degrees of freedom of the robot in question, which implies a possibility of inputting information into the robot control system and more particularly a possibility of modifying certain points of the paths stored by the robot. Such robots are generally expensive.
The object of the invention is to propose a simple and economic device, which can be adapted to most robots not having means for receiving control signals from the outside.